The origin of khondalites: geochemical evidence from the Archean to Early Proterozoic granulite belt in the North China craton

Abstract

The dominant rock types in the khondalite suite in the Archean to Early Proterozoic granulite belt of north-central China are sillimanite-garnet gneiss (SGG), quartz-garnet gneiss (QGG), and quartz-feldspar gneiss (QFG). Field and geochemical results from the China khondalites and khondalites from other locations (including those from the type locality in India) are not consistent with a paleosol protolith. Major and trace element distributions in the SGG and QGG suggest shale and feldspathic sandstone protoliths, respectively. REE distributions including negative Eu anomalies in both rock groups are remarkably similar to those in Phanerozoic shales. Element distributions in QFG, including highly fractionated REE patterns, are similar to Archean TTG and these rocks are interpreted to have felsic volcanic protoliths.

Sediment protoliths of the SGG and QGG may have been derived from sources in which granite and a smaller amount of basalt dominated, but they cannot have had significant contribution from Archean TTG sources. The China khondalite protoliths appear to have been deposited in a cratonic basin along the northwest margin of the North China craton. Although the khondalites from China and elsewhere chiefly have sedimentary protoliths, different compositions and lithologic proportions between khondalite suites indicate variable sediment provenance, intensity of paleoweathering, and tectonic settings.